1. Field of the Invention
This invention relates to spin-pack assemblies wherein fiber-forming material is filtered just before being spun into filaments. More particularly, it concerns a cartridge filter for use in such spin-pack assemblies.
2. Description of the Prior Art
Spin-pack assemblies wherein fiber-forming material is filtered just upstream of the spinneret capillaries are well known in the art. For example, U.S. Pat. No. 3,896,028 discloses a spin-pack assembly for use in melt spinning of polymers into filaments. Similar assemblies are known in which solutions of polymers are fltered immediately upstream of the spinnerets prior to wet or dry spinning of the fiber-forming material into filaments.
A typical spin-pack assembly has a chamber within which a filter medium is contained between screens. The inlet to the chamber is in communication with a source of supply of the fiber-forming material and the outlet of the chamber is in communication with the spinneret capillaries. The screens are usually of a very fine wire mesh.
In a commonly used commercial operation, the filter portion of the spin-pack assembly is made up by laying an exit screen on a support grid at the exit of the chamber. Then a filter medium, such as the powdered sintered metal disclosed in U.S. Pat. No. 3,896,028, is poured into the chamber and a second screen is placed atop the filter medium. However, with such a filter, difficulties are encountered in assuring that the exit screen is seated properly and that no by-passing of fiber-forming material or filter medium occurs around the edges of the exit screen. To assure better sealing around the edges of the exit screen, a ring of soft, deformable metal is swaged atop the exit screen and against the wall of the chamber. However, this too has not been entirely satisfactory. Pieces at the edge of the screen sometimes break off and fall into the spinneret capillaries. Also, replacement of such filter assemblies and repeated swaging can cause undesirable wear on the chamber wall and deformation of the support grid. In addition, when the filter holder contains more than one chamber, such as is often the case in dry spinning of filaments wherein a dozen or so chambers are located in the same holder, nonuniform loading of the filter medium and contamination of the spinneret capillaries with fine, broken pieces of the screen or with filter medium powder can occur. Furthermore, the handling of the loose, powdered filter medium, screens, etc. and assembling the materials into the filter holder chamber involve costly and time-consuming operations.
In view of the difficulties with prior-art spin-pack assemblies, it is an object of the present invention to provide a filter which is assembled separately and fitted into the spin assembly holder easily, quickly and without any loose filter medium powder contaminating other parts of the pack.